On free team board, a team member who is not a board member can remove this board from team.

[Dmitri Afanasjev]

I have a user A and a user B

I have a team created with free plan by user A. 

User A created a team board, set its visibility to Team Visible.

User A invited user B to the team, but did not invite him to the board.

User B can now view board, but cannot edit anything in it EXCEPT he can remove that board from team, which is kind of a disruptive action by someone who was not even a part of a board.

[Irwan Ambak]

I have a similar problem where I as a Team Member am accidentally removed by another Team Member. How can I recover from that?!

[Iain Dooley]

@Dmitri Afanasjev use user B added to the team as an admin or normal member?

[Dmitri Afanasjev]

Yes, user B is an admin. I believe there is no way to add team member not as an admin with free team plan.

[Iain Dooley]

@Dmitri Afanasjev yes you can:

[Dmitri Afanasjev]

I am pretty sure I cannot without upgrading to business plan 

[Iain Dooley]

@Dmitri Afanasjev oh right, looks like I made this team before they brought in those changes. The screenshot I sent is from a free team, but they must be applying the above restriction to new teams.

[Dmitri Afanasjev]

Yeah, and this creates the situation described above...